1. Field of Invention
This invention relates generally to optical spectroscopy and more particularly to the deployment of hybrid lasers comprising semiconductor-pumped, small- or micro-cavity fiber lasers having a wide operating spectrum that includes multiple wavelengths in the hybrid laser output that substantially match wavelength spectral characteristic features of analytes supporting the noninvasive measurement of analyte concentrations in a specimen analyte such as, for example, but not limited to, glucose, urea, alcohol, cholesterol or bilirubin in human tissue.
2. Description of the Related Art
Optical spectroscopy techniques are becoming increasingly important for a variety of applications for remote and non-invasive sensing. Within the medical health field, there is an extensive effort underway to develop the capability to non-invasively, and in real time, monitor the concentration of blood constituents, also referred to as analytes, such as alcohol, cholesterol, glucose, blood oxygen level or other such blood components. In particular, the ability to monitor the blood glucose concentration in a noninvasive manner would provide a tremendous benefit to the millions of people suffering from diabetes, which requires careful monitoring and control of blood glucose levels. Such a noninvasive approach is painless and does not require penetration of the skin to obtain or draw a blood sample. In order to perform the required spectroscopy to extract concentrations of blood constituents, current technology will typically use a broadband radiation source to illuminate the sample under test, either in-vivo or in-vitro, and couple radiation transmitted through or backscattered from the sample into an optical spectroscopy unit in order to extract information about the chemical composition of the illuminated material. Such a system is shown, for example, in U.S. pat. No. 6,574,490 and the references cited and discussed in that patent. Also mentioned in patent '490 are infrared spectroscopy methods employing infrared radiation either in an absorption mode or a reflective mode relative to analyte sample under examination. As a particular example, analytes, such as glucose, cholesterol, alcohol or oxygen content in the blood, will absorb differently, relative to absorption coefficient across the infrared spectrum. Since there are many different kinds of identifiable analytes in the sample, their absorption characteristics will overlap and vary differently from one another across the infrared spectrum and beyond such that there is no real reliable way to determine one analyte from another without some way of focusing, for example, on distinguishing intensities as wavelength spectral characteristic features along the characteristic optical spectrum of the analyte. However, how to accomplish, in a successful manner, the differential determination of these spectrum differences relative to one analyte over another in a sample in quick and simple way has eluded many of those skilled in the optical spectroscopy art, particularly since any system employed would have to successfully evaluate a plurality of intensities for a particular analyte to successfully achieve a reliably accurate measurement and final determination of its concentration on a continuous and speedy basis. Also, conventional infrared absorption spectroscopy is hampered by the intrinsic background absorption of water in the infrared spectrum that has strong absorption at spectral characteristic features of similar spectral characteristic features of a blood analyte. Water is nearly 95% of the human body. For example, glucose as an analyte has absorption spectrum peaks in the range of about 1,800 nm to 3,400 nm. But water also has a high and varying absorbance in this region and, therefore, can represent a constant and serious interference in determining the concentration of glucose in an in vivo specimen. Consequently it is very challenging to extract accurate measurements of the concentration of a specific blood analyte in the presence of interferences both from varying concentrations of other blood analytes and the strong and dominant absorption due to the presence of water. In summary, the optical spectroscopy art has yet to fully realize a low cost, noninvasive, highly portable analyte sensor which has the clinical accuracy required for widespread adoption.
The above mentioned prior art approaches are also cumbersome resulting in large and relatively inefficient measuring systems. The employment of a white light source consumes considerable power, much of which is not in the spectral ranges of interest. The spectrometer is inherently a large device with complex mechanical, or at best electro-optical, mechanisms that are sensitive to ambient conditions and poorly suited to applications where monitoring is desired in small clinics, homes, or as a small portable or wearable unit.
Thus, there is need for a noninvasive optical spectrometer system that provides for a compact and portable unit, such a palm unit, that will illuminate a subject sample or analyte at a signal set of pre-determined absorption wavelength features, collect these radiation signals from the result of scattering, reflection and/or absorption by the analyte to be analyzed, and provide for the precise determination of the relative strengths of the various spectral components of the collected signals relative to their respective initial signal strengths prior to impinging on the analyte. Therefore, there is further need for an effective radiation source that can provide multiple wavelength signals all sensitive to distinguishing wavelength spectral characteristic features, such as intensities of an analyte across a wide absorbance spectrum, which is also sufficiently compact and versatile to be of pocket size or employed in an in vitro manner or embedded in an in vivo manner. There is a further need for such a device to be based on a set of technologies that are capable of being readily manufactured at low cost and providing medically high reliability on a repeated basis of use.